Study of the decay ϕ→f0(980)γ→π+π−γ with the KLOE detector

We measured, with the KLOE detector, the spectrum of π+π− invariant mass in a sample of 6.7×105e+e−→π+π−γ events with the photon at large polar angle (θγ>45°) at a centre of mass energy s around the ϕ mass. We observe in this spectrum a clear contribution from the intermediate process ϕ→f0(980)γ. A sizeable effect is also observed in the distribution of the pion forward-backward asymmetry. We use different theoretical models to fit the spectrum and we determine the f0 mass and coupling constants to the ϕ, to π+π− and to KK¯.